Process of making electric conductors



oct. 13, 1936. R MAUTSCH 2,057,242

PROCESS OF MAKING ELECTRIC CONDUCTORS Filed May 29, 1935 2 Sheets-Sheetl Oct. 13, 1936. R. MAUTscr-xv PROCESS OF MAKING ELECTRIC CONDUCTORSFiled May 29, 1955 2 Sheets-Sheet 2 Patented ct. 13, 1936 y UNITEDSTATES PROCESS 0F MAKING ELECTRIC CONDUCTORS Robert Mautsch, Brussels,Belgium,

assignor to Manufacture Generale Metallurglque, Socit Anonyme, Brussels,Belgium, a Belgian com- Diny Application May 29, 1935, Serial No. 24,112In Belgium June), 1934 8 Claims.

This invention refers to the manufacture of insulated electricconductors, such as heating resistances, and of cables for powertransmission, which comprise a core and a sheath or sleeve, both ofconcentric tubular shape, separated by one or more annular layers ofnonconductive material, in which the heating wire is embedded in thecase of a heating resistance. It is very important that the insulatingmaterial of these conductors should be well compressed between the coreand the sleeve, especially in the case of heating resistances in whichthe insulating material is exposed to disaggregation under the action ofhigh temperatures and to the strains of expansion and contraction of theheating wire. It has already been suggested l that the insulatingmaterial could be ccmpressed by causing the conductor to be drawn out orlaminated, which process has for effect, the re-tightening of thesleeve, but only at the price of lengthening it, which causes thedisplacement of the insulating material, and is only practicable whensuch material is in pulverulent or plastic form.

In accordance with the present invention, the in situ compression of theinsulating material of the conductor is assured by expanding the tubularcore by a mandrel, by hydraulic pressure, or by any other suitablemeans.

The expanded tubular core presses the insulating material forcefullybetween it and the sleeve, without causing any appreciable deformationin the aggregation ofthe conductor. If this latter be composed of aheating wire wound in the insulating material, this wire will be firmlyheid by the compressed insulating material, and there can be no play,even under the effect of vibration or violent shocks. In addition, thedielectric coefiicient and the thermal conductivity of the insulatingmaterial are increased by the compression. If the insulated conductor isintended to. be used as a cable for power transmission, the compressionof the insulating material will give to it, qualities. ofwater-tightness and of dielectric rigidity, which are very favourable toperfect insulation of the core through which the electric current ispassed.

According to a preferred method cf carrying out my invention, I avoidthe use of binding agents or other materials capable of givingcombustion products liable to soil and lower the quality of theinsulating material. To this end, I apply the insulating material linsheet form and I subject said sheets, without binding agent,

to a preliminary compression while it is being applied, i. e. before thetubular core is expanded. To effect this preliminary compression l usethe conductor itself, while it is being wound. I then surround thewinding with a further insulating 5 layer which in turn is tightlycompressed by winding around it a metal wire or strip forming a tightwrapper band.

When there are a plurality of concentric conductors, each conductor isused for compressing l0 the' underlaying insulating layer, and anencircling band or wire is tightly wound around the whole element. Thisencircling band is `intended not only to compress the parts enclosedthereby, but also to expel the air from the sul5 Fig. 1 shows inperspective, a section of an electric heating resistance partiallystripped in o order to show the concentric elements.

Fig. 2 is a view of a longitudinal section of a portion of resistance,illustrating the process of expansion.

Fig. 3 represents, in longitudinal section. two 35 portions of a tubularcable joined end to end. Fig. 4 shows a cable Joining at right angles,Fig. 5 is a cross-section of a cable with sev eral conductors.

Fig. 6 illustrates the winding of insulating o material in sheet form.

Fig. 7 is a longitudinal section of a complete element with sheetinsulation.

Figs. 8 and 9 are respectively an elevation and a corresponding planview, on scale, showing the winding of the insulating sheets and of thewire for compressing same.

In Figs. 1 and 2, the heating resistance consists of a. tubular core Iof malleable metal, as

for example, a copper tube, on which is placed 50 an insulating sleeve2, for example oi mica or mica composition, around which the resistancewire 3 is Wound helically. A second insulating sleeve 4 surrounds thewire 3 and the whole is placed in a tubular sheath or sleeve l, advnu asmaller 45 tageously composed of a harder metal than the core I, forexample, of steel.

As these various elements may be readily slid one into the other, theprocess of manufacture is very easy. In order iirmly to unite theelements and to compress the insulating body on to the resistance wire,the malleable inner tube is expanded. For this purpose, a fluid may beintroduced under pressure, or, as is shown in Fig. 2, an expanding ,tool6 may be drawn through the tube I, the diameter of the tool beinggreater than the original diameter of the tube. It will be understoodthat the expansion of the core I compresses the insulating bodies 2 and4 against the internal wall of the sleeve 5. The insulating material isforced between the turns of the resistance wire 3, which are thusdefinitely locked in position. Neither the disaggregation of theinsulating material through heat, nor the expansion or contractionstresses of the heating wire, nor vibrations nor exterior shocks cancause any loosening, so that all risk of overlheating or of fusion byhot points, or by contact of the convolutions of the wire, iseliminated.

The tubular resistance may be used to heat a circulating liquid, as welloutside of the sleeve ,5 as inside of the core I. It may be iitted lwithiins or arranged in vany suitable manner in a heating apparatus.

In Figs. 3 and 4, which show an electric cable inI accordance with theinvention, III is the tubular core of the cable,.for example a coppertube, II is an insulating sleeve placed over the core, and I2 is thetubular metal sheath or sleeve, which surrounds the whole. As in thecase of the resistance described above, the tubu- Vlar core I0, which,in this case, serves as the conductor, in the proper sense of the word,is suitably expanded to compress the insulating material II between itand the sleeve I2. 'I'he compression of the insulating material preventsthe presence of empty spaces or of air pockets in the insulation of thecable and assures absolute water-tightness.

Two portions of cable manufactured in this manner may be electricallyconnected end to end in a. very simple way, by means of pins I3 ttedinto their cores I0, and the joining may be tightened by means of a ringI4 screwed on the joined extremities of the sleeves I2. A water-tightfitting I5 completes the joint.

In the case of an angle joint, as is shown in Fig. 4, a pin I3 tted intothe core I of one of the portionsof the cable is made with an eye I6clamped around the stripped core of the other portion, and the whole isplaced in a junction box I'I welded at I8 to the sleeve i2.

Fig. 5, shows a cable with a plurality of concentric tubular conductorsI0, Ill' and I0", which is made by expanding, in the iirst place, thetube I0" in the sleeve I2, then the tube I0 in the tube I0" and finally,the tube I0 in the tube I0'. y Referring to Figs. 6l and '7, I is thetubular core, of copper or other malleable metal, 2 the iirst layer ofinsulating material, 3 the conductor, for example a resistance Wire orstrip tightly wound` around the layer 2, and 4 is the second insulatinglayer, 2li4 is an encircling wire or strip which is tightly wound aroundthe insulating layer 4, and 5 isthe outer tube which forms a protectingsheath for the whole element.

In order to compress the successive layers of insulating material I mayadvantageously operate as follows.

The tubular core I being rotated and being simultaneously movedlongitudinally in the direction of the arrow a (Fig. 9) on a suitablesupport (not shown), I apply thereon the first insulating layer whichcomprisessheets 2, for example of mica, fed by a belt 2| which isrotated by a pulley 22. v

In immediate proximity to the belt 2l, I feed the resistance wire from aspool 23 situated on theside of the core I remote from the pulley 22. Asshown in Fig. 6, the wire 3 is wound on the core I in overlappingrelation tothe sheets 2, in such manner that as soon as a sheet isapplied on the core it is caught by the wire 3 which holds it in placeand presses it with a pressure that may be adjusted by means of a.stretching device 24.

The insulating layer 2 and the resistance wire 3 being wound, the sameoperation is repeated with the outer insulating layer 4 and theencircling band 20. The whole then is forcibly introduced into thesheath 5 and subjected to internal pressure, for example by means of amandrel, which tightens all the parts' togetherl and uniformlydistributes the stresses in each layer. They concentric layers then canno longer become loosened under the actionof vibrations or jars.Moreover the dielectric coemcient and the thermal conductivity of theinsulating material are increased by the compression. v

It will be understood that these qualities are also preserved when theelement comprises more than two insulating layers and that theadvantages ofthe invention obtain, whether it be applied to heatingreslstances or to cables for power transmission.

I claim:

1. A process of producing insulated electric Iconductors, comprisingsurrounding an expansible tubular core with insulating material, tightlywinding an electric conductor around said material, thereby subjectingsaid material to permanent pressure, surrounding the wound conductorwith more insulating material, surrounding the whole with a sheath andexpandlng said core by an internal pressure.

2. A process of producing insulated electric conductors, comprisingsurrounding a malleable tubular core with a layer of insulatingmaterial, winding an electric conductor around said insulating layerthereby compressing same, surrounding the wound conductor with an outerlayer of insulating material, winding a band around said outer layer tocompress same, surrounding the whole with an outer sheath, and passing amandrel through said core to expand same and compress vthe partscomprised between said core and said sheath.

3. A process of producing insulated electric conductors, comprising .anexpansible tubular core with a plurality of superposed-insulatinglayers, tightly winding an electric conductor between every twosuccessive insulating layers thereby successively subjecting each saidlayer jecting said layer to compression by winding an electric conductortherearound, surrounding the wound conductor with a further insulatinglayer, subjecting said further layer to compression by winding anencircling band therearound, inserting the whole in.an outer sheath andsubjecting said tubular core to internal pressure.

5. A process of producing insulated electric conductors, comprisingWinding sheets of insulating material on an expansible core, pressingsaid sheets into position by tightly winding an electric conductortherearound, winding sheets of insulating material around the woundconductor, pressing said sheets in position by tightly windingtherearound a compressing band, surrounding the whole with a sheath, andexpanding said core by internal pressure.

6. A process o.' producing insulated electric heating resistances,comprising winding sheets of insulating material on an expansibletubular core and simultaneously winding an electric resistance wire inoverlapping relation to said sheets, thereby encircling said insulatingsheets with the winding of said wire and subjecting said sheets tocompression, then again winding sheets of insulating material on theresulting product and simultaneously winding under tension a pressureresisting band in overlapping relation to said last mentioned sheets,inserting the whole in a sheath and expanding said core by internalpressure.

7. A process of producing insulated electric heating resistances,comprising rotating an expansible tubular core and simultaneously movingsaid core longitudinally, winding sheets of insulating material on saidrotating core and simultaneously winding under tension a resistance Wirein overlapping relation to said sheets, then winding around theresulting product sheets of insulating material and simultaneouslywinding under tension a metal strip in overlapping relation to the lastmentioned band, inserting the whole in a sheath and expanding said coreby internal pressure.

8. A process of making insulated heating resistances comprising windingsheets of insulating material on an expansible tubular core, tightlywinding a resistance wire around said sheets, thereby subjecting saidsheets to inward pressure and causing any air entrapped therebetween toescape, winding sheets of insulating material around the resultingproduct, tightly winding encircling wire around the last mentionedsheets, thereby subjecting them to inward pressure and causing any airentrapped therebetween to escape, inserting the whole in a Sheath andpassing a mandrel through'said tubular core, thereby subjecting thewhole to an outward pressure and securing the previously -compressedparts within said outer sheath.

ROBERT MAUTSCH.

